Odd MPG drop for my 5.3

[rudapa]

I just took the truck on a road trip from Nebraska to Tennessee. First on a positive note there was only a slight hint of "shaking" at 75 to 80 MPH on a couple road surfaces. For the vast majority of the trip it ran smooth from 70 to 85 MPH. Now on the MPG thing.

 

I got good mileage IMO on the way down with the 1st leg of the trip giving me 19.6 avg (NE - MO) with speeds mostly running 75 to 80. I got 18.8 MPG running from Nashville to Harriman on I40 and I had the cruise set at 85 MPH. I thought that was really good especially considering a pretty good cross wind. Now for the funny part. I was averaging over 20 MPG running around Rockwood and Spring City, but then I filled up at the Rocky Top in Rockwood, TN and my mileage on the same roads I was averaging 20 MPG dropped to 17 MPG and I got crap mileage all the way home averaging 16.5 MPG running 75 to 85. I did have a lot of head winds running home, but this is an extreme drop. I'm not sure what the deal is????

 

[BillWho]

In a word, ethanol. It drops the energy content per gallon. Take a look at this chart and it is clear how much less energy per gallon is available in E85 fuel. Let's say you have half a tank of non-ethanol content gas and you fill it to full with E85. The btu content goes from about 114,000 btus per gallon to about 97,000 but, a 13% drop in energy per gallon. Multiply .87 times 20 mpg and you get about 17.3 mpg.

 

http://en.wikipedia.org/wiki/Gasoline_gallon_equivalent

 

Personally, I wish they would keep the corn for feeding livestock and not for feeding our trucks.

[rudapa]

I've never run any E85. Only 10% 87 and once 89 octane...........

[Jon A]

Even a pretty mild headwind could cause that much drop. I wouldn't worry about it.

[BillWho]

I would have quoted the example using E90, but the chart only showed the energy content of E85. I'm guessing the original poster was down to about a 1/4 tank and filled it with E90 and with the 3/4 tank of E90 mixing with the original non-ethanol gas put the energy content down to the 17 mpg range.

 

I drive altogether about 30,000 miles a year in my Acura and Sierra. Out of curiosity I re-set my gas gauge every time I re-fill just to see if the fuel was E90 (or worse still, E85). You truly see a noticeable mpg drop with the ethanol/gas blends.

[bigdeer1]

U should be happy.... I see 14 mpg everywhere. But I woulda bought a Prius for gas mileage

[rudapa]

U should be happy.... I see 14 mpg everywhere. But I woulda bought a Prius for gas mileage

 

Yea but I went with the sweet interior and Bose system over the better 0 to 60 times from the ecoboost and hemi offerings for the MPG as well. I was getting excellent mileage until that tank of gas from Rocky Top which I thought was odd. Wind is a factor as is the outside temp and they are both possible explanations for the drop in MPG driving back to Nebraska, but the mileage dropped while I was in Tennessee and the air temp and wind was not a factor there.

[BillWho]

Ethanol, it was the culprit. Blame it on the government, not your truck.

[ms55330]

Just did a trip out to ND last week and found that the mileage was very sensitive to temp and wind. I had the millage thing set to the 25 mile average, the cruse set to 80 in rolling hills and all the fuel along the whole trip was 10% ethanol.

-10 to -20 little wind 14 mpg

0 to +10 little wind 17 mpg

+10 15mph tailwind 20 mpg

 

can't wait to see what I get on a summer trip

[rudapa]

I would have quoted the example using E90, but the chart only showed the energy content of E85. I'm guessing the original poster was down to about a 1/4 tank and filled it with E90 and with the 3/4 tank of E90 mixing with the original non-ethanol gas put the energy content down to the 17 mpg range.

 

I drive altogether about 30,000 miles a year in my Acura and Sierra. Out of curiosity I re-set my gas gauge every time I re-fill just to see if the fuel was E90 (or worse still, E85). You truly see a noticeable mpg drop with the ethanol/gas blends.

 

E85 = 85% alcohol and normal fuel = maximum 10% ethanol......... Just for clarification.............I've never seen E90 nor have I ever used E85.

[BillWho]

E85 = 85% alcohol and normal fuel = maximum 10% ethanol......... Just for clarification.............I've never seen E90 nor have I ever used E85.

Umm, you may not thought you have bought ethanol containing fuel, but you have, most assuredly. In my county here in the middle of NC, there are only four pumps (out of probably 300 pumps) that flat out say the fuel does not contain ethanol. Three of the pumps are 87 and one pump is 93. Those stations charge a higher price for specially certified and delivered non-ethanol content fuel. Folks who go boating in our area know about those stations with the guaranteed no ethanol fuel. Boaters that know go to those pumps to fill up as boat tanks that sit for months with ethanol are natural harboring places for the bugs that make gooey stuff that is bad for our boat motors. The rest of the pumps here have the standard sign: "may contain ethanol".

 

Yessiree, ALL of us have most assuredly been buying gas containing ethanol. We just don't know when we have gotten E90 or E85 until we see the reduced mpg.

[BillWho]

The first link is for gas stations selling ONLY pure gas. According to this list the Rocky Top in Rockwood is not a pure gas only station.

http://pure-gas.org/index.jsp?stateprov=TN

 

Here is a controlled driving experiment that found E85 to have 26% less mpg than pure gas:

http://www.edmunds.com/fuel-economy/e85-vs-gasoline-comparison-test.html

[newdude]

Sounds like maybe a bad batch of gas and the headwinds?

[rudapa]

Umm, you may not thought you have bought ethanol containing fuel, but you have, most assuredly. In my county here in the middle of NC, there are only four pumps (out of probably 300 pumps) that flat out say the fuel does not contain ethanol. Three of the pumps are 87 and one pump is 93. Those stations charge a higher price for specially certified and delivered non-ethanol content fuel. Folks who go boating in our area know about those stations with the guaranteed no ethanol fuel. Boaters that know go to those pumps to fill up as boat tanks that sit for months with ethanol are natural harboring places for the bugs that make gooey stuff that is bad for our boat motors. The rest of the pumps here have the standard sign: "may contain ethanol".

 

Yessiree, ALL of us have most assuredly been buying gas containing ethanol. We just don't know when we have gotten E90 or E85 until we see the reduced mpg.

 

I'm using ethanol all the time and never said I wasn't, but it is clearly marked on the tank as "up to 10%" ethanol. I've never purchased E85 which is also clearly marked at the pump because not all vehicles are "flex fuel" rated. I've NEVER used E85 in my truck. I've only ever seen two offerings for ethanol and it is up to 10% or 85%.....................

 

I will try some 93 octane (no ethanol) and see how it does for a comparison. Nebraska is one of a hand full of states where the law requires the pumps mark each pump if it contains ethanol and 93 is available in many locations here alcohol free.

 

I've never seen E90 (90% ethanol) gas at any pump anywhere............

[BillWho]

Rudapa, my sincerest apologies! Thank you for correcting my error. It is E10 and E15 fuel that we traveling folks have been buying.

http://en.wikipedia.org/wiki/Common_ethanol_fuel_mixtures

 

This blows a hole in my earlier calculations, but still, in my road warrior travels on trips, I have seen sizable drops in mpg after re-fueling, so there is something about the fuel that is different and I always associated it with ethanol. The above link says that the energy loss with 10% ethanol is around 1% lower mpg so I am stumped now as to what else it could be when I am moving down I-95 in flat Florida and see a difference in mpg after re-fueling.